Production of abrasive material



PatentedUct. 29, 1.940

y lPitopUC'rIoN oFYABRAsIvEvMATEnIAL n y v FrankyJ.A Tone, Niagara Falls, N. Y., assignoriby f mesne assignments, to TheCarborundum Company, Niagara. Falls, N.. Y.z,",a 'corporation of g Delaware Applicationbecember 31, 1935, Serial No;.56;8413. I

' fzclaims'.) (c1.l al1-218)? This invention relates to the production of coated flexible abrasivev articles Whereinthere is employed a'backing material containing a'pluralityofla'yersr- I" f -Coated abrasives of thecharatenwith which:`

' thisinventionis concerned have been employed in'the manufacture'of abrasive discs which are commonly used on portable grinders for various purposes suchas 'smoothing down metallic welds.

Due to the manner in-which such' discs are used,it 4isnecessary that 'the'ibacking thereof'.v

shall haveacertain degree of rigidity or stillness and yet r which shall be capable yof: repeated flex-` ing,fsince the discs are pressed-againstV the Workl to a degree which .causes contact with the "work on an area only about 1`"wide at theperiphery of the discs. Since thediscsareoperated'at speeds upwards of 2000 R. P. M.,'fthey must be capable of `alternately bending-Sand straightening out at the same rate and for considerable periods of time. It will therefore be seen that -discs which are to be subjected to such r treatment mustpossess'the ability to` be repeatedly exed while they are under considerable side pressure resulting from the contact of the disc with the work.

Heretoforeit has been customary to make-such discs bycombining .a heavy grade of cloth with a particular type of cellulosic material commonly referred to as 'vulcanized'ber or hydrolized cel- 0 lulose. -This combining is accomplished by coating the surfaces vwhich are tobe joined together with glue, uniting the two surfacesfand'then subjecting the article to' a careful treatment :for drying out the' glue. A fter the backing hasbeen thus prepared, it is coated with abrasive grains ing abrasive coated paper 'or cloth.

Vulcanized ber and the method used to combine it with 'the cloth areboth expensive and the discs -are therefore correspondingly costly. Furthermore, since glue cannot be heated much and glue in the manner shown inthe art of linakabove F. without destroying its'strengthfa'n'd since a. combination backingunited-'with glue puffs up v`and becomes entirely useless if lheated much above this point,'such backings'f'are entirely unsuited for abrasive products wherein-there isl employed a binderfor theabrasive grains which requiresheat treatment'above 150-F. f

It is "accordingly an object ofthe'present invention to provide a backing materialy whichv shall not be open to the objections enumerated above.

Itfi's also an object of the invention to providey a coated `'abrasive article whichsh'all have the properties required vof discs' as `detailed above and which shall be 'relativelyinexpensiva Another VwhichI lmay combine, I employ vas a-jbinderforV d a `number oi, such ma'tterialsl which .are suitable.

object of '-the inventlonis-to porvide an improved method for making-coated abrasive articles.

In carrying out-my invention' Ifmay employ any of anumber of Vkinds ofr backingv material which are toJbeunitedinto-a 'composite backing.'y Forl example, I mayuse a "combination" of a heavy grade 'of cloth with'v'certain specialgrades of pa` per or I may usea lighter grade "of-cloth and Iv may even use vulcanized ber in certain special cases where discs are subjected .to unusuallyse- 10 vere treatment. y I may also use vcombinations of s variousA cloths or combinations lof various papers.`r Thebackin'g` material maybe other materials than cellulosic such as: paper orcloth. Forexample,v sheetsof densehomogeneous organic ma-' terial such` asf resins andwcellulosic derivatives may .be-used.. Sheetlmetals such assheetsteel 'y mayalsobeused. .-f v Regardless of the types-of backing materialsuniting these backing layers into a composite ar-f ticle'- a material which is capable of being softenedwhen heatedto a temperature whichwll notinjure the backingmaterial used.- :There are for. example. certaincopolymers of vinyl chloride and .vinyl acetate which are marketed under vari- 7 ous trade names such. as Vinyloid or Gelva; similar vinyl polymersv which haveibeen lsubse.-

quently reacted with acetaldehyde orformalde- 30 hydeicellulose'ester lacquers which comprise aA Y' celluloseester such as cellulose nitrate or acef' tate dissolved ina suitable solvent. usually modied with a plasticizing agent and ,containinga resin to promote adhesion; Lpolymerizedl s'tyrol or vinyl benzene, sometimes called meta "styrene, l whichfmay be modiiied by plasticizing orflexi' bilizingagents if desired. In general there; may be used'materials of. this kind whichfhave the property. ofl softening and becoming flexible when heated' and hardening again when cooled to .normal temperatures.- g"

In making up :my .new'backingmaterial I'lmay .y use any convenient methodfor applying the binder materiall to the backing, as for example, by spreading on a solution of the binder by .means of a roll inthe v.manner commonly employedl inl making abrasive paper, or by spraying. Orl'. may

use the binder in the form of a powder mwhich case I preferably moisten the surface of the backing material to which the powder is to be applied, n' as for example, bywetting the backingwithwater orwith a solvent for the backing binder and then dusting on the powdered binder in a conventional manner. 55

- berelatively stiff and inflexible, I choose such backing materials and employ lsuch a quantity of binder that the completed backing shall be of the desireddegree of stiffness.

These binders If thefcombining operation does not warm thev resin suilicientlytorender the1 resulting backing sufficiently flexible or i! it is desired to have time elarse betweenthe manufacture of the backing and the coating operation the backing may be ilexibilized beioreuse-by warming. `Thiswarm- 1 lng maybe done to a roll which has been wound up from-a backing :as made ,inf the combining machine. 'or the backing-may be fedfrom the combining machine through a heated chamber.

Howeverthe combining step may be such that vit is warmed to the requiredy degree in the combining machine. l f f Having rendered. the backing material flexible,

either'in the combining operation orr separately, I then coat it with'abrasive grais and a binder for the grains, in any convenient manner as car- 5 riedf out inthe usual abrasive paper-coating machine. As is Well/known inthe art, this method' comprises passing the backing betweenl the socalled pressure'roll and the adhesive roll which ispartially immersed in a vat of adhesivaand then' sprinklingy abrasive grains onto the adhesivecoated side of the backing. A subsequent sizing coat of adhesive may be, and usually is, ap-

plied over the abrasive grains to fix them more rmly on the backing. "Other suitable methods of coating may also be used, e. g.,'spreading a mixture of adhesive and grain on the backing, or spraying the making or sizing coats, or both, onto the backing.

The inventioirwill be further described with reference to the accompanying `drawing,-.wherein: Figure 1 is a side view of `an abrasive coated article made in accordancewith the invention;

Figure 2 is a diagrammatic sidesection of apparatus suitablefor use in carr'ying out the in- Figure 3 is a diagrammatic side section'ofap'- paratus suitable for use in carrying out the invention; and Y j Figure 4-'is a `diagrammaticside section of ap- `paratus suitable ,for carrying out the invention.

' Referring to the drawing, the coated abrasive article illustrated in Figure 1 comprises a backing material consisting of a layer I of` cloth cemented to a-layer 2 of cellulosic material by a layer 3 of thermoplastic cement. The combination` backe, at room-` temperature, sol 15 non-resilient that the backing so stiilas'to be tional spray-gun.

ing is coatedl with abrasive grains 4 which are attached to the cloth side of the backing by a binder 5.

In Figure 2 I haveillustrated apparatus adapted for combining two layers of backing material. In this drawing the roll of cloth 6, mounted on a spindle 1, isfed between adhesive roll 8 and pressure roll 9. yThe adhesive roll Bris partially submergedin a body of adhesive I4 contained in a -vat i5. The coated web than passes over a heat- 10 ing Aelement I0 and meets a web II of cellulosic material supplied from a roll I2 which is mount- 1 ed ony a spindle' I3'. The heating element I0 is provided with suitable terminals I8 and 20 which areconnected to a source of electric potential. 15 The web oi cellulosic material and the adhesive coated clothare passed between rolls I6 and I1,

whereby the twolayers of backing material are pressedtogether, and then wound up into a ro1lI8. v M l Passage of the adhesive. coated web over the heating element causes evaporation of thevsolvent from the adhesive I4 and warms the adhesive to an extentsuiiicient to cause it'to become iirmly attached to thecellulosic material II and 25 also keeps thel adhesive suflicientlyy flexible-so that the subsequently formedbackingmaterial canbe woundr into a suitable yroll I8. l

In Figure 3 I have illustrated a method of coating my combination backing with abrasive grains. 30

iReferring to this drawing, the backing .material, *wound4 into a roll I8, 'suitably warmed to ilexibilize the backing.` adhesive I4, is fed between a-grain binder roll 2l and a pressure roll 22. The roll ZI is partially submerged in an adhesive 2335 which iskept in avsuitable vat r24. Rotation of` the roll 2lv causes a coating of adhesive to be applied-to the under sideof thebacking material andthe moving backing materialis then vpassed around van idler roll 25 and under a grain feed 40 hopper 26. IThe hopper 28 is provided. with a gate 21 for adjusting the ilow of abrasive grain to a grain feed roll 23. The abrasive grain fed from the hopper by the grain feed apparatus falls onto the abrasive coated web 'and thecoated web 45 then passes aroundidler-rolls 29, 30, 3I, 32 and 33. to a suitable festooning apparatus of a type commonly used in the manufacture of abrasive coated webs. The festooning apparatus permits the storage `of-a relatively large quantityl of coat- 50 ed material for a time suiiicient to harden the adhesive to a point. where the abrasive coated article can be wound up into a roll 34.

The abrasive coated web may be later given an additional coating of adhesiveto attach the 55 abrasive grains more rmly to the backing in apparatus similar to that described in Figure 3 orby other suitable means, as for example, by sprayingon a sizing coating withthe conven- The production of a composite backing'material and the steps of coating it with abrasive and adhesive maybe carried, out continuously in a suitable apparatus. Referring to Figure 4, I

' have illustrated one apparatus winch may be used 65 formaking and coating the conripositel backing in successive steps. A webof ,cloth 6r which .is rolledon spindle 1 isunrolled and coated with thermoplastic `adhesive by passing it vover fountain roll.v 8., The coated web is then Joined to a 70 web I2 ofcellulosic material such as paper which isr rolled ona Vspindle I3. Thismaterialis unrolled-and passed, together with the coated cloth, between rolls I1 'and- I8 4which press the ywebs together to cause them to adhere and form a com- 75 andresfn 1li mixeagso1vents--riie'eiothlig uien; warmed. to remv'efmo'st` o f. ythe solvent,f fed 'l through calenderrolls 'along with the web of 1 posite sheet The composite. sheet then passes overr fountain roll 2| whichputs thereon a coate ing of the adhesive to be. used for xing. abrasive grainv onthe sheet. Abrasive grain is supplied 5 from hopper 26 and the sheet or. web is pulled by suction roll 31 toxthe Iestooning apparatus` l5 curing of the adhesive for. the abrasive material the;backing may be permitted-tobecome-cool and stiff during the curing' operation, afterwhichit is warmed to ilexibilize it before removal from- .the festoons or before winding up .on suitable lo r011s F After the backing has been suitablycoated with abrasive grains the abrasive coated backing vis subjected -to a suitable'after-treatment to .set up the adhesive.; Where Athe `adhesive requires 5 a treatment. for the evaporation of. a solventthis treatmentA consists in maintaining the article in f a chamber suitably controlled as totemperature so as to dry out thebinder tothe desired degree,

and wherer, a; heat.; hardenable binderfor vthe 0 grains is used, the article-is heat treated to cure the binder.

treatment in that form,l or the web Vof coated 35 abrasive maybe cut up into suitable shapes such as discs, and the individual, discsvsuitably treat ed accordingto a procedure which is commonly employed inthe 'manufacture of abrasive discs.

The materials which may be used for my .inven- 40 tionincludethe papers, vcloths and adhesives ordinarily used in making abrasive coated paper and cloth, However the following examples illustrate the inventiony as applied to the manufacture of sheet material for the manufacture of abrasive discs.

Example I heat and caused to stick to both the cloth and the paper and unite them into Va composite arti# cle. The composite backing is then fed directly into an abrasive paper-making machine and they cloth side of the backing coated with a normally liquid phenolic condensation product resin and abrasive grains, following which a sizing coating of liquid resin is sprayed onto the coating.

The thus formed article is heat treated at 180 F. for two hours to partially set up the liquid resin rain binder, following which discs arefcut from he web and subsequently cured at 250 F. for six hours to complete the hardening of the grain binder.

Example II A grade of cloth of the character described in Example I is coated with a cellulose ester lacquer in the form of a solution of cellulose ester This after-treatment may be ap plied tothe material while suspended as festoonsf or it may bewound ingrolls and-subjected tothe paper as described in Example 4 1, and thenwound up .into a roll.. Thiscomposite backing is` rather stiandginexible,at ordinary room .temperay Example IVII Cloth o# the I'is coated *with* a solution of-a thermoplastic al'- character described in 'Example'v kyd resin, resulting from thereaction offglycol f and afdibasicacid. The clothfis warmed to remove most of the lsolvent and passed between heated` calender rolls with paper to form a' com-` the coating stickyl andis then passed between heated rolls withpaper to press the,` cloth' and paper togethertoform a composite sheet.

.Ifthebacking thus formed is not used immediately it maybe permitted-to cool 'and warmed when wantedfor use byputting itin an oven at. 200 FLY Whens`oft enough it is' coated with abrasive grains land abinderin the mannerdescribed in Example I,' tl ie bind,c'erbeing an'airdrying 'varnish con'ip'risingany oil-modiedphenolic'f'resin taken up 'in 'a vdrying' oil andthinned withsoiv'entj j '1 "i i Y.The abrasive :b'ated "n'iaterial i's then further treated to setup thegrain binden'andutup into loth of a' 'suitablecharacter -is coatedwith a solution of .a thermoplastic resin resultingf'rom, the polymerization of' methyl methacrylate. The

clothvis warmedto evaporate solvent. and' make discs, after -which -iurtherf"treatmentA may be given to lcompletethe hardeningfof the binder.v

As indicatedabove, by selecting, a suitable back? l ing binder and suitable thickness, vit is vpossible to prepare a backing having the required properties of'stifness and iiexibility so that thecoated backing will be suitable for use in discs of the character described. '-It is thuspossible to vary selectively the flexibility in avseries of related articles of this nature whereby a backingv material having the exibility desired for the work may be selectively produced. 'Ihis may be done by selectively modifying the properties of the backing binder by the addition of suitable agents such as plasticizers like tricresyl phosphate, dibutylphthalate or a non-drying oil such as castor oil. On the other hand, binders which are not stiff enough can be modied by including inertV illers such as pulverized int or they can be mixed with kheathardening resins which are set up in the subserquent heat treatment of the abrasive coated articles. Selective yvariation of the flexibility may also be accomplished by selecting different resins having the desired properties. For example, a`series of alkyd resins of varying flexibility may be used.

applyingv a layer of binder ef The method of producing composite material having a desired degree of flexibility is not lirnited to the use of thermoplastic resins but may include also the use of heat hardenable resins of varying ileXibiIity. For example heat harden-V able glycerol-dibasic acidalkyd resins may be used. A series of resins of varying flexibility may i e Vbe prepared by mixing glyceryl phthalate and glycolsuccinat'e in varying ratios. In addition 1 fiexibilizing agents may be addedt to certain resins in varying proportions to'- produce resins of varyingflexibi-lity; for example, m-dinitrobenzene, and high boiling solvents such as diethyl l. phthalate, triacetin, and` aniline; `Series of resins y1oA -binder of the same or of a diierent character as oiuniformly varying flexibility; may befused to*4 produce a series of composite sheets-of"uniform' `lyivaryting flexibility. v'

\Asii`1dicated irl the specific eirarnplearone type of backing binder and a different typeof abrasive grain binder may be used; or the two binders'may be of the same general character: Likewise, it isv possible, to employ thesame kind oi' binder in the making .or rst lcoat of grain?` adhesive, and a a second or sizing;coat,:which isapplied after the abrasive grains have been attached; tothe back-V ingby the making coat. l t

As indicated in the discussionV of therprior art, my'invention has a number of` advantages; `For example, it makes itpossible to use cheaper man terials inthe backing than the vulcanized ber which has `been"heretofore]erriployed. Itfals'o makesit possible.to use binders for the' yabrasive grain v-which require heat' treatment and which cannotbe used in combination with backings `united with glue." Furthermore j it provides la f method of making backings having any desired degree of iiexibility'.;

My improved backing alsqhasthe advantage that it canA be readilylflexibilized by merely heatg ing. This is not true of backings'fwhich employ heat hardening resins as the backing binderA because such resinsdo ,not soften under heat and when the backing `hasorice `beerrcornbin'ed and treated to set upjthe 'resirito' a point where it is no longer sticky', tcannot be made sumcient-` 1y flexible so that it can be'passed through Vthe usual abrasive papermaking machine. l

As indicated, myrinventionfis adaptable' to a number'of modifications andlembodiments, and

is not t0 be limited tothe specicexamples men'- tioned." `y' V I claim: j

is relatively stiff and rigid in its own plane but is' 1. The methodof making a 'coated article which capable of being repeatedlyfexed by the applica-l tion of lateral lpressure -which'comprises ad-v hesvely uniting a vplurality of Webs of backing` material by means of a cement which is relatively stiff and inflexible atvordinary temperatures but -capable ofk being` made flexibley and plastic by heating Vand of being n alternately vheated. and cooled without causing a separation of the'layers 'of backing material; thereby forming a composite web which-is so stii, at ordinary, temperatures.

that it cannot be'passed through:l an abrasive paper-coating machine but which can be flexibilized by heating to make it capable of Abeing so passed, maintaining vthe composite webv at a temperature such that thewebis flexible, passing the i web through an abrasive paper-coating machine and coating it with abrasive and adhesive, `and.

ing a separation of the layers of backing mate-1 rial, thereby formingacomposite -web whichis so' stift at ordinarytemperatures that it cannot be passed through-a`n abrasive paper-coating ma.

chine but which caribe ilexib'iliziedby` heating'to l make it capable 'of-being so' passed, heating the composite web toa temperature such that thel web is ilexible,passingtheweb' through an abra'- sive paper-coating machine and" coating it withabrasive and'adhesive, and coolingthe abrasive` 

